But a growing awareness of a need for water efficiency has prompted Pepsico to set itself a bold target.

Within 10 years, it wants to achieve zero water intake at the Walkers' sites, starting with the Leicester location, eliminating the need to bring mains water onto the site.

Measuring

But knowing where to cut down water requires knowing exactly how much is used and where. If you don't measure it, you can't change it, says Mr Flanaghan, between greeting everyone on the floor personally.

Spuds are just like us. Every time they hit something, they bruise

Pete Flanaghan, sustainability manager, Pepsico UK and Ireland

He uses one seemingly insignificant step in the crisp making process to illustrate his point.

"You see that dish?" he says, pointing to the small surface inside a cylinder. Water hits the dish before spraying evenly on to sliced potatoes to remove excess starch.

"That used to be a teaspoon shape. But what happens when you run a tap onto a teaspoon?" he asks rhetorically. "It flies off in all directions, unevenly."

By changing that one design, water is saved, he says.

Changing attitudes internally is also crucial to reduce water wastage, adds Mr Flanaghan.

"We've had leak busters," he says.

Training sessions were held with staff to raise awareness of the need to cut water wastage. It involved identifying leaks and quickly taking action to rectify them.

It sounds naff," he confides, "but it has worked."

Farming

Elsewhere, a trip to farmer James Daw in Staffordshire, a long-time supplier to Walkers, reveals an increasing awareness of water usage in the growing phase.

"The thing about potatoes is the detail," says Mr Daw, as we visit a recently-harvested potato field.

If water has to be added - to supplement rainwater - sensors in the ground relay exactly how much to avoid unnecessary drenching.

"It all boils down to more crop per drop," explains Martyn Seal, sustainability director for Pepsico International's European region.

Potato paradox

And yet there seems to be an inherent paradox in potatoes.

EMBEDDED WATER

Item

Litres per unit

Size of unit

Litres per kg

Sheet of paper

10

A4 sheet of 80gsm

2000

Cup of tea

30

250ml

2400

Apple

70

100g

700

Cup of coffee

140

125ml

21,000

Bottle of beer

150

500ml

300

Slice of bread

440

400g

1100

Chicken fillet

683

175g

3900

Packet of sugar

1500

1kg

1500

Chunk of cheese

2500

500g

5000

Packet of rice

3400

1kg

3400

Beef steak

3875

250g

15,500

Pair of jeans

10,850

1kg

10,850

While 75% of a spud is water, turning them into crisps is basically about removing the water, says Mr Seal, lowering his spectacles.

What goes in at the growing stage has to be taken out at the processing stage.

"Potatoes are a very thirsty crop," explains David Wilson, an agro-manager for Pepsico UK and Ireland, who co-ordinates farmers including Mr Daw.

"A challenge is how to reduce the water content," says Mr Daw knowingly, pointing to muddy potatoes as they rumble along a conveyor belt on the farm.

Walkers is involved in a pilot scheme, involving academics from Nottingham University, to capture water extracted from potatoes during slicing and frying, treat it and reuse it, says Pepsico's Mr Seal.

When asked what would make the optimal spud, Mr Seal looks almost dreamy.

It must be reliable to process, of a high standard and good for crisps, he says.

If a potato could contain less water, this could have other benefits.

Less energy would be needed to dry and fry the potatoes, which would lower emissions and costs.

Research

Pepsico UK and Ireland is also working with the Scottish Crop Research Institute to investigate new potato varieties that would contain less water.

The firm is also investing in research into irrigation, to compare the effectiveness of different systems and conserve water.

It is right we should think more about water. We, after all, are the custodians of the land

James Daw, farmer, Staffordshire

Climate change affects seasons and rainfall, so more drought-resistant crops will be needed. But Mr Seal is quick to add that developing new varieties of potatoes can take years.

Such concerns seem a long way off as the moist earth squelches underfoot in the farm, testimony to another wet week.

But multinational firms such as Pepsico are having to assess operations globally, and there is growing stakeholder pressure to do so.

James Daw applauds this. "It is right we should think more about water. We, after all, are the custodians of the land."

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